This application claims priority from the following applications:
International Application No.: EP992002527, filed Jan. 27, 1999.
1. Field of the Invention
The present invention relates to methods and apparatus for a general cross-connect switching device and more particularly to a general switching method for the cross-connecting of an arbitrary number of communication lines, e.g. optical fibers, carrying an arbitrary number of channels.
2. Description of Related art Including Information Disclosed Under 37 CFR 1.97 AND 1.98
According to an article by C. A. Brackett, A. S. Acampora, J. Sweitzcr, G. Tangoman, M. T. Smith, W. Lennon, K. Wang, and R. H. Hobbs, entitled xe2x80x9cA Scalable Multiwavelength Multihop Optical Network: A Proposal for Research on All-Optical Networksxe2x80x9d IEEE Journ. Lightw. Techn., Vol. 11, pp.736-753, 1993, several signals are transmitted simultaneously over a single optical fiber by multiplexing the different signals on different carrier wavelengths referred to as xe2x80x9cWavelength Division Multiplexingxe2x80x9d (WDM).
WDM networks consist of different WDM optical connections, each of which consists of several fibers carrying WDM signals, and of optical cross-connects to switch between the different links. An example is schematically shown in prior art FIG. 1. The lines all represent optical waveguides, often fibers, with WDM signals. The optical cross-connects (OXC) preferably have the following functionality:
individual channels from each fiber can be dropped (for use in a local access network e.g.),
individual channels (coming from the local access network) can be added to each fiber,
individual channels from each fiber can be switched to any other fiber.
Different wavelength channels from one fiber may be switched to different output fibers. In some cases, one also requires that the individual channels can be converted in wavelength so that wavelength contention can be avoided if two channels with equal wavelength have to be switched to the same output fiber.
A typical architecture of an optical cross-connect, with Nf incoming fibers and Nf outgoing fibers, is depicted in prior art FIGS. 2A and 2B. Reference is made to M. S. Borella et al., xe2x80x9cOptical Components for WDM Lightwave Networksxe2x80x9d, Proc. of the IEEE, Vol. 85, pp. 1274-1307, 1997, E. lannone, R. Sabella, xe2x80x9cOptical Path Technologies: A Comparison Among Different Cross-Connect Architecturesxe2x80x9d, IEEE Journ. Lightw. Techn., Vol. 14, pp. 2184-2196, 1996 and J. Zhou et al., xe2x80x9cCrosstalk in Multiwavelength Optical Cross-Connect Networksxe2x80x9d, IEEE Journ. Lightw. Techn., Vol. 14, pp. 1423-1435, 1996. The cross-connecting functionality is achieved by first demultiplexing signals on the incoming fibers into the individual channels, by subsequently space switching all the individual wavelength channels, possibly followed by wavelength conversion (FIG. 2B) and by finally multiplexing or recombining the switched individual channels. Different variations of this architecture have been proposed in the literature. However, they all more or less are based on the same principle and they all require an N-dimensional space switch, with N being the product of the number of incoming and outgoing fibers and the number of wavelength channels per fiber. For example, a cross-connect device may be provided wherein all fibers are first demultiplexed before switching.
In most of the optical cross-connects of the type shown in FIGS. 2A and 2B, the optical filters can have a fixed wavelength dependence. There are then Nfxc3x97N1 such filters, with Nf being the number of input and output fibers and N1 the number of wavelength channels per fiber. Furthermore, if full connectivity is required (i.e., it must be possible to connect two channels with equal wavelength from different input fibers to the same output fiber by making use of wavelength conversion), a total of Nf(Nfxe2x88x921)xc3x97(N1)2/2 elementary 2xc3x972-switches are required. An alternative, however, is to use tuneable optical filters (which can filter any of the wavelength channels), in which case only Nf(Nfxe2x88x921)xc3x97(N1)/2 elementary 2xc3x972-switches are required. If no wavelength conversion is used and only connections between the different fibers are needed for the individual channels (meaning that for each individual channel at the input a connection with all output fibers is necessary), then Nf(Nfxe2x88x921)xc3x97(N1)/2 elementary 2xc3x972-switches are required.
The main drawback of conventional cross-connect devices is the number of components (filters, switches) needed.
A cross-connect device with Nf input fibers and Nf output fibers, where Nf is an even number can be built as a combination of smaller cross-connects with two input and two output fibers. This is illustrated in prior art FIG. 3 for the case of four input and four output fibers. In this figure, OXC-2,2M) stands for an optical cross-connect with two input and two output fibers, with each fiber carrying 2M wavelength channels. The notation 2xc3x972 OXC represents an optical cross-connect device with two input and two output fibers.
It should be emphasized that the discussion above is not limited to optical systems. Switching in electrical communication systems exploiting frequency division multiplexing (FDM) shows the same characteristics. Frequency channels in electrical communications are equivalent in this respect to wavelength channels in optical systems.
Therefore, it is an object of the invention to provide cross-connect devices and methods comprising less components than presently available devices.
Another object of the present invention is to provide a cross-connect switch and a method of operating the same which provides full connectivity while reducing the cost of the device.
The present invention is a cross-connect switching device for use with all types of communication systems including optical and for receiving a multiplicity of input and output line Nf with reach input and output line carrying N1 channels. The cross-connect switching device of this invention is capable of switching any one of the Nfxc3x97N1 input lines to any one of the Nfxc3x97N1 output lines with Nfxc3x97N1 being equal to or greater than four (4) and where the channels are equally distributed over the input lines.
The invention comprises a switch which is connected to selected ones of the input lines of the cross-connect switching device and which is adapted to switch a channel group or group of channels on one input line of the switch as a block or group to one of the output lines. A channel group is defined as a plurality of channels up to a maximum of N1 channels.
There is also included a partial demultiplexer which is also connected to the switch which relates at least one individual channel from one of the channel groups, and a combiner unit for combining the selected individual channels onto an output line of the cross-connect switching device.
Additional channel groups may be generated by including another switch connected between the partial demultiplexer and the combiner unit which receives the output of the partial demultiplexer and switches an additional channel group as a block towards another one of the output lines of the cross-connect switching device.